1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __ASM_ALTERNATIVE_MACROS_H
3 #define __ASM_ALTERNATIVE_MACROS_H
4 
5 #include <asm/cpucaps.h>
6 
7 #define ARM64_CB_PATCH ARM64_NCAPS
8 
9 /* A64 instructions are always 32 bits. */
10 #define	AARCH64_INSN_SIZE		4
11 
12 #ifndef __ASSEMBLY__
13 
14 #include <linux/stringify.h>
15 
16 #define ALTINSTR_ENTRY(feature)					              \
17 	" .word 661b - .\n"				/* label           */ \
18 	" .word 663f - .\n"				/* new instruction */ \
19 	" .hword " __stringify(feature) "\n"		/* feature bit     */ \
20 	" .byte 662b-661b\n"				/* source len      */ \
21 	" .byte 664f-663f\n"				/* replacement len */
22 
23 #define ALTINSTR_ENTRY_CB(feature, cb)					      \
24 	" .word 661b - .\n"				/* label           */ \
25 	" .word " __stringify(cb) "- .\n"		/* callback */	      \
26 	" .hword " __stringify(feature) "\n"		/* feature bit     */ \
27 	" .byte 662b-661b\n"				/* source len      */ \
28 	" .byte 664f-663f\n"				/* replacement len */
29 
30 /*
31  * alternative assembly primitive:
32  *
33  * If any of these .org directive fail, it means that insn1 and insn2
34  * don't have the same length. This used to be written as
35  *
36  * .if ((664b-663b) != (662b-661b))
37  * 	.error "Alternatives instruction length mismatch"
38  * .endif
39  *
40  * but most assemblers die if insn1 or insn2 have a .inst. This should
41  * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
42  * containing commit 4e4d08cf7399b606 or c1baaddf8861).
43  *
44  * Alternatives with callbacks do not generate replacement instructions.
45  */
46 #define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled)	\
47 	".if "__stringify(cfg_enabled)" == 1\n"				\
48 	"661:\n\t"							\
49 	oldinstr "\n"							\
50 	"662:\n"							\
51 	".pushsection .altinstructions,\"a\"\n"				\
52 	ALTINSTR_ENTRY(feature)						\
53 	".popsection\n"							\
54 	".subsection 1\n"						\
55 	"663:\n\t"							\
56 	newinstr "\n"							\
57 	"664:\n\t"							\
58 	".org	. - (664b-663b) + (662b-661b)\n\t"			\
59 	".org	. - (662b-661b) + (664b-663b)\n\t"			\
60 	".previous\n"							\
61 	".endif\n"
62 
63 #define __ALTERNATIVE_CFG_CB(oldinstr, feature, cfg_enabled, cb)	\
64 	".if "__stringify(cfg_enabled)" == 1\n"				\
65 	"661:\n\t"							\
66 	oldinstr "\n"							\
67 	"662:\n"							\
68 	".pushsection .altinstructions,\"a\"\n"				\
69 	ALTINSTR_ENTRY_CB(feature, cb)					\
70 	".popsection\n"							\
71 	"663:\n\t"							\
72 	"664:\n\t"							\
73 	".endif\n"
74 
75 #define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...)	\
76 	__ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg))
77 
78 #define ALTERNATIVE_CB(oldinstr, cb) \
79 	__ALTERNATIVE_CFG_CB(oldinstr, ARM64_CB_PATCH, 1, cb)
80 #else
81 
82 #include <asm/assembler.h>
83 
84 .macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
85 	.word \orig_offset - .
86 	.word \alt_offset - .
87 	.hword \feature
88 	.byte \orig_len
89 	.byte \alt_len
90 .endm
91 
92 .macro alternative_insn insn1, insn2, cap, enable = 1
93 	.if \enable
94 661:	\insn1
95 662:	.pushsection .altinstructions, "a"
96 	altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
97 	.popsection
98 	.subsection 1
99 663:	\insn2
100 664:	.previous
101 	.org	. - (664b-663b) + (662b-661b)
102 	.org	. - (662b-661b) + (664b-663b)
103 	.endif
104 .endm
105 
106 /*
107  * Alternative sequences
108  *
109  * The code for the case where the capability is not present will be
110  * assembled and linked as normal. There are no restrictions on this
111  * code.
112  *
113  * The code for the case where the capability is present will be
114  * assembled into a special section to be used for dynamic patching.
115  * Code for that case must:
116  *
117  * 1. Be exactly the same length (in bytes) as the default code
118  *    sequence.
119  *
120  * 2. Not contain a branch target that is used outside of the
121  *    alternative sequence it is defined in (branches into an
122  *    alternative sequence are not fixed up).
123  */
124 
125 /*
126  * Begin an alternative code sequence.
127  */
128 .macro alternative_if_not cap
129 	.set .Lasm_alt_mode, 0
130 	.pushsection .altinstructions, "a"
131 	altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
132 	.popsection
133 661:
134 .endm
135 
136 .macro alternative_if cap
137 	.set .Lasm_alt_mode, 1
138 	.pushsection .altinstructions, "a"
139 	altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f
140 	.popsection
141 	.subsection 1
142 	.align 2	/* So GAS knows label 661 is suitably aligned */
143 661:
144 .endm
145 
146 .macro alternative_cb cb
147 	.set .Lasm_alt_mode, 0
148 	.pushsection .altinstructions, "a"
149 	altinstruction_entry 661f, \cb, ARM64_CB_PATCH, 662f-661f, 0
150 	.popsection
151 661:
152 .endm
153 
154 /*
155  * Provide the other half of the alternative code sequence.
156  */
157 .macro alternative_else
158 662:
159 	.if .Lasm_alt_mode==0
160 	.subsection 1
161 	.else
162 	.previous
163 	.endif
164 663:
165 .endm
166 
167 /*
168  * Complete an alternative code sequence.
169  */
170 .macro alternative_endif
171 664:
172 	.if .Lasm_alt_mode==0
173 	.previous
174 	.endif
175 	.org	. - (664b-663b) + (662b-661b)
176 	.org	. - (662b-661b) + (664b-663b)
177 .endm
178 
179 /*
180  * Callback-based alternative epilogue
181  */
182 .macro alternative_cb_end
183 662:
184 .endm
185 
186 /*
187  * Provides a trivial alternative or default sequence consisting solely
188  * of NOPs. The number of NOPs is chosen automatically to match the
189  * previous case.
190  */
191 .macro alternative_else_nop_endif
192 alternative_else
193 	nops	(662b-661b) / AARCH64_INSN_SIZE
194 alternative_endif
195 .endm
196 
197 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)	\
198 	alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
199 
200 .macro user_alt, label, oldinstr, newinstr, cond
201 9999:	alternative_insn "\oldinstr", "\newinstr", \cond
202 	_asm_extable 9999b, \label
203 .endm
204 
205 #endif  /*  __ASSEMBLY__  */
206 
207 /*
208  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
209  *
210  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
211  * N.B. If CONFIG_FOO is specified, but not selected, the whole block
212  *      will be omitted, including oldinstr.
213  */
214 #define ALTERNATIVE(oldinstr, newinstr, ...)   \
215 	_ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
216 
217 #endif /* __ASM_ALTERNATIVE_MACROS_H */
218